Most of those — 975,000 — signed up in the month of December. The deadline for signing up and receiving coverage by Jan. 1, was Dec. 24.

Tavenner writes:

"Our HealthCare.gov enrollment nearly doubled in the days before the January 1 coverage deadline compared to the first few weeks of the month. December enrollment so far is over 7 times that of October and November. In part, this was because we met our marks on improving HealthCare.gov: the site supported 83,000 concurrent users on December 23rd alone."

The site, of course, has been plagued by crippling issues that made it nearly impossible for some Americans to sign up for health care in the early days. The numbers Tavenner provides are intended to show that the site is working a lot better.

"The figures tell only part of the story. The administration has yet to provide a December update on the 14 states running their own exchanges. While California, New York, Washington, Kentucky and Connecticut have performed well, others are still struggling.

"Still, the end-of-year surge suggests that with HealthCare.Gov now functioning better, the federal market may be starting to pull its weight. The windfall comes at a critical moment for Obama's sweeping health care law, which becomes 'real' for many Americans on Jan. 1 when coverage through the exchanges and key patient protections kick in."

Altogether, the administration had predicted that 3.3 million Americans would sign up for health care via federal and state marketplaces by the end of the year.